This invention relates to low profile lighting and to LED lighting powered by mains AC electricity. The invention also relates to a combination of such lighting. Indeed, in one embodiment, it relates to a form of LED low profile lighting that in thickness is not much thicker than a typical two-core mains electricity cable that delivers electrical power to the lighting. For example, it may be less than 10 mm thick and in one embodiment is less than 8 mm thick.
Such low profile lighting finds application in many situations where the protrusion of a light from the surface to which it is attached is desirably kept to a minimum. One such situation is in room lighting where the light fitting is desirably flush or negligibly protrusive from a ceiling or wall on which the light is affixed. In this case, cabling to the light typically passes through an aperture of the ceiling or wall and the fitting covers the aperture, masking the cable. Another situation applies in kitchens and workshops where wall-mounted cupboards or units whose lower surface is below normal eye level and is above a work surface or other structure to be illuminated by a light connected to the undersurface of the wall unit. Here, the cable is often pinned to the lower surface so that it enters the side of the light fitting. The difference between these two situations is based on the fact that behind the surface of a wall or ceiling a concealed duct exists or can be provided to lead wiring to the light fitting, whereas in the case of light under a wall cupboard, no such duct generally exists and it would not be desirable to lead the wiring through the interior of the cupboard space.
In this specification, unless the context otherwise dictates, the terms “light”, “lighting” and “light fitting” are used interchangeably with reference to the same thing.
Low-profile lighting is known, per se, and indeed employing LED lights. For example, AU-A-2004/00417 discloses lighting comprising a channel-shaped housing for fixture below a wall cabinet, a printed board mounting LED devices and a lens cover. However, there is no description of the power circuit, which presumably comprises a traditional separate low voltage supply such as a mains transformer.
An object of the present invention is to provide such low-profile lighting, but where the need to locate a separate power supply is avoided without loss of the minimal profile.
Thus, in accordance with a first aspect of the present invention there is provided a light comprising:                mating front and back housings, between them defining a one-dimensional thickness of the light;        an attachment of the back housing, whereby the light is attachable to a base on which the light is to be mounted;        a circuit board mounting circuit elements and interconnecting conductive tracks to which LED devices are connected; and        a minimum power-rating two-core mains electricity cable passing through one of a side aperture and a back aperture of said housings, the conductors of which cable are fixed of said circuit board; wherein        the circuit board is enclosed and sandwiched between said front and back housings;        said front housing transmits light emitting from said LED devices;        said circuit elements and LED devices are arranged to be powered by AC mains electricity; and        said one-dimensional thickness is no greater than 25% more than the sum of the thicknesses of said front and back housings and the power cable, and not less than the thickness of said cable, wherein        said housings define a rim region of the light surrounding the circuit elements on the circuit board, and wherein        labyrinth flanges are formed on one of said front and back housings in said rim region whereby said cable, on passing into the light through one of the apertures, passes along a labyrinthine path around said rim defined by said labyrinth flanges.        
By “one-dimensional thickness” is meant simply the thickness of the light in one dimension. Essentially, this means the minimum separation of two parallel solid surfaces between which the light may be disposed. However, this excludes non-essential extensions beyond such dimensions. “Non-essential” means here that the element of the light (if any) that extends beyond the minimum separation is not essential to operation of the light but is simply a design choice without essential functional significance.
By “thickness” of the front or back housing is meant the thinnest dimension of each component that covers the majority of its area and is primarily responsible for excluding the electrical components of the light from contact with users or extraneous components. Such insulation cannot be less than the minimum thickness required to make the product safe. Mandatory safety standards relating to domestic electrical products (such as BSEN 60335 and the like) require products that have no independent safety earth wire to have live parts insulated from accessible surfaces by two independent insulation barriers each at least 1 mm thick or one single reinforced insulation barrier 2 mm thick.
Preferably, the cable has a maximum dimension and a minimum dimension of its cross section and said one-dimensional thickness is no greater than 25% more than the sum of the thicknesses of said front and back housings and the maximum dimension of the power cable, and wherein the cable is arranged between said front and back housings with its maximum dimension extending between said housings.
Alternatively, the cable may be arranged between said front and back housings with its minimum dimension extending between said housings, in which event and said one-dimensional thickness is no greater than 25% more than the sum of the thicknesses of said front and back housings and the minimum dimension of the power cable.
Said one-dimensional thickness is preferably less than 10% more than the sum of the thicknesses of said front and back housings and the maximum dimension of the power cable.
Said one-dimensional thickness is preferably less than 10 mm and preferably less than 8 mm.
Said fixing may be by direct soldering of said conductors to pads on the circuit board. Said side aperture may be separate from said rear aperture, whereby selection of through which aperture the cable passes is made by disassembling the light and passing the other end of the cable, being the end not connected to the circuit board, through the desired aperture and reassembling the light. In this event, unless disassembly of the light opens both the side and back apertures, no plug can permanently be fixed on said other end of the cable and the light must obviously be capable of disassembly. Disassembly can, however, be arranged to open both apertures if each is formed by both the front and rear housings so that separation of them opens each aperture. It is preferred, in any event, that the light is capable of disassembly and to this end the front and rear housings may be interconnected by screws.
Said front housing may have bosses in said rim region and said rear housing may have corresponding screw holes through which screws may pass and engage with said bosses to connect said housings together.
The cable may be arranged in said labyrinthine path with its conductors on a line joining said front and rear housings in the direction of said one-dimensional thickness of the light, and said cable is bent about an axis parallel said line by said flanges sufficiently to create a strain relief for said cable. Preferably, after exiting said labyrinthine path, the outer sheath of the cable ends and said conductors are turned to lie in a plane substantially parallel said front and back housings and pass over an edge of the circuit board to said pads.
Alternatively, said cable may be arranged in said labyrinthine path with its conductors on a line parallel said front and rear housings, and said cable is bent by said flanges about an axis perpendicular said line sufficiently to create a strain relief for said cable.
Preferably, said attachment by which the light may be attached to a base comprises an elongate thin sheet bracket having holes to receive two screws, which holes are on opposite sides of said rim region, said base housing including two screw recesses in said rim region to accommodate the heads of screws connecting said bracket to a base and a shallow recess across its back surface between said screw recesses to accommodate the bracket, whereby the light when connected to the bracket lies flush against a base to which the bracket is connected.
Preferably, said bracket comprises tabs at its ends adjacent to said holes, and said recesses are elongate in a circumferential direction and have windows at one end, whereby, said tabs are receivable in said recesses and, on rotation of the light, said tabs enter said windows to lock the light with respect to the bracket. Said bracket may be sheet metal and resilient.
However, said attachment may comprise apertures in said back housing, and bosses in said front housing coincident with and passing through said back housing, said bosses being adapted to receive screws by which the light may be attached to a surface.
Preferably, said front housing has a central region that is opaque that covers circuit element regions of the circuit board that do not include said LED devices, and a peripheral translucent or transparent region that covers LED device regions of the circuit board. Preferably, said central and peripheral regions of the front housing are surrounded by said rim region. Said peripheral region may comprise an open region of the front housing, the front housing having a cover recess to receive a transparent or translucent cover covering and closing said peripheral region.
However, said front housing may have a central translucent or transparent region that covers LED device regions of the circuit board, the rim region being extended around said central region and covering circuit element regions of the circuit board that do not include said LED devices. In this event, said central region may comprise an open region of the front housing, the front housing having a cover recess to receive a transparent or translucent cover covering and closing said central region.
Preferably, said light is a round disc in outline, where the thickness of the disc comprises said one-dimensional thickness.
In one embodiment of the present invention, the back housing and circuit board are integrated into a combined single element that performs both the functions of back housing and circuit board.
Circuits are known for powering LED devices from mains AC supply. U.S. Pat. No. 5,936,599 and WO-A-2004/038801 disclose banks of paired diodes in anti-parallel configuration driven by an AC power source so that each diode is illuminated when current flows through it during alternate ones of the AC power phases. Thus each LED is illuminated for about half the time and is switched 50 or 60 times per second (depending on the AC source). Flickering is an inevitable consequence of this arrangement. It is an object of the present invention to provide an improved circuit.
Thus, in accordance with a second aspect of the present invention there is provided a light comprising a circuit board mounting circuit elements and interconnecting conductive tracks to which LED devices are connected in a circuit, wherein said circuit comprises:                a mains voltage AC input;        two banks of said LED devices arranged in anti-parallel across said AC input;        a capacitative voltage dropper comprising a capacitor and resistor in series with said banks; and        an inductor in series with said capacitative dropper to limit surge current on switch on.        
Preferably, two inductors are provided, one connected to each terminal of said AC input.
Preferably, a discharge resistor is connected in parallel with said capacitor.
Preferably, a current limiting variable resistor is connected across said AC input in parallel with said banks of LED devices, capacitative voltage dropper and inductor.
Preferably, said first and second aspects of the present invention are combined and said circuit boards of each aspect are one and the same circuit board.
In this event, said circuit elements are preferably surface mount components.
Preferably, said capacitor comprises two capacitors in parallel. Preferably, said anti-parallel banks are arranged in said peripheral region surrounding said central region with one bank around one side and the other bank around the other side of said peripheral region.